The present invention relates to a chemical mechanical polishing carrier head that includes a flexible membrane, and associated methods.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the exposed surface of the substrate becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
One accepted method of planarization is chemical mechanical polishing (CMP). This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a moving polishing surface, such as a rotating polishing pad. The polishing pad may be a “standard” polishing pad with a durable roughened surface or a “fixed-abrasive” polishing pad with abrasive particles held in a containment media. The carrier head provides a controllable load to the substrate to push it against the polishing pad. A polishing slurry, which may include abrasive particles, is supplied to the surface of the polishing pad.
Some carrier heads include a flexible membrane with a mounting surface that receives the substrate. A chamber behind the flexible membrane is pressurized to cause the membrane to expand outwardly and apply the load to the substrate. Many carrier heads also include a retaining ring that surrounds the substrate, e.g., to hold the substrate in the carrier head beneath the flexible membrane. Some carrier heads include multiple chambers to provide different pressures to different regions of the substrate.